The invention generally relates to wireless communication systems. In particular, the invention relates to processing data at the physical layer for such systems.
In wireless communication systems, data received from the network is formatted for transfer over the wireless interface. Conversely, data received over the wireless interface is processed to recover the original network data. The processing of this data is referred to as physical layer processing.
Processing data at the physical layer is a complex operation in wireless communication systems. FIG. 1 is a conceptual illustration of physical layer processing for the proposed time division duplex (TDD) mode for wideband code division multiple access (W-CDMA) of the proposed third generation partnership project (3GPP). The processing is shown for the transmitter. In an analogous reverse manner, the data is processed at the receiver. However, one difference with physical layer processing at the receiver is that the receiver typically processes soft symbols complicating the processing requirements. FIG. 1 also pertains conceptually to the uplink of the frequency division duplex (FDD) mode of W-CDMA. However, the parameters used by each block differ between TDD and FDD.
Transport blocks arrive for transport over the wireless interface. The transport blocks arrive in sets of transport block sets. The sets are received in a specified time interval, known as transmission time interval (TTI). For the TDD mode, and FDD mode the possible TTI lengths are 10 ms, 20 ms, 40 ms and 80 ms, which correspond to 1, 2, 4 and 8 radio frames, respectively. A circular redundancy code (CRC) attachment block 42 attaches CRC bits to each transport block. The CRC bits are used for error detection at the receiver. The CRC bit length is signaled from higher layers.
The transport blocks (TrBlks) are serially concatenated by the TrBlk concatenation/code block segmentation block 44. If the number of bits of the concatenated blocks is larger than the maximum size allowed for a code block, the concatenated blocks are segmented. A channel coding block 46 error correction encodes the code blocks, such as by convolutional coding, turbo coding. After encoding, the code blocks are concatenated together. If the concatenated code blocks can not be segmented into a minimum number of equal sized segments (frames), radio frame equalization is performed by concatenating additional arbitrary bits by a radio frame segmentation block 50.
A first interleaver 48 interleaves all the concatenated data. Subsequently, the interleaved data is segmented into radio frames by a radio frame segmentation block 50. A rate matching block 52 punctures or repeats bits. The puncturing and repeating assures data transmitted on each physical channel equals the maximum bit rate for that channel. The rate matching attributes for each transport channel (TrCH) is signaled by higher layers.
The TrCH multiplexing block 54 receives one frame's data for each transport channel. The received data for each TrCH is serially multiplexed onto a coded composite transport channel (CCTrCH). A bit scrambling block 65 scrambles the CCTrCH bits.
A physical channel segmentation block 58 maps the multiplexed data onto the physical channels. A second interleaver 60 interleaves the scramble data either over the entire radio frame or over each time slot. After second interleaving, the interleaved data is segmented into the physical channels for transport over the air interface by a physical channel mapping block 62.
The data for each physical channel is spread using a respective code by a spreading block 64. The spread data is scrambled using a scrambling block 66 with a code associated with the base station. Each resulting scrambled chip is pulse shaped by a pulse shape filter 68. A frequency correction block 70 adjusts the frequency of the resulting signal. The frequency corrected signal is radiated through the wireless interface.
For the downlink of FDD mode as also shown in FIG. 1, the processing is performed in a similar manner conceptually. However, there are some differences. In the FDD downlink, rate matching is performed after the channel coding by a rate matching block 52. As a result, radio frame equalization is not performed. To support discontinuous transmission, a first discontinuous transmission (DTX) indication is inserted prior to first interleaving by a first DTX indication block 72 and a second DTX indication is inserted prior to physical channel mapping by a second DTX indication block 74.
Two approaches for performing physical layer processing are a software based approach and a hardware based approach. In a software based approach, the bulk of the physical layer processing is performed by software. A software based approach allows for great flexibility. Parameters of the physical layer processing can be easily changed by software revisions.
Two drawbacks with a software based approach are that: 1) processors, such as microprocessors or DSPs use higher power than customized solutions, and 2) several processors may be needed to carry out all the required functionality.
A hardware based solution allows for a reduction in total chip area required and reduced power consumption. Customizing and configuring the hardware for a particular environment, results in better efficiencies in the data processing. However, such an approach reduces the flexibility of the design. Reconfiguration of the physical layer processing is limited to parameters made available in the initial design.
Accordingly, it is desirable to have a physical layer processing which allows for high processing speed and flexibility.